NO310545B1 - Process for depyrogenating injectable solutions of pharmaceutical formulations with contrast agents, pre-pyrogenation equipment and depyrogenic diagnostic solutions - Google Patents

Description

The present invention relates to a method for depyrogenation of injectable solutions of pharmaceutical formulations with contrast agents for diagnostic imaging, equipment for depyrogenation of these solutions and depyrogenated injectable diagnostic solutions. Typical of these solutions is an extremely high degree of purity with regard to low contents of bacterial endotoxins.

It is known that injectable formulations of pharmaceutical products or diagnostic reagents must satisfy strict criteria for sterility and pyrogenicity in order to be administered to patients with acceptable safety margins. Accordingly, it is of fundamental importance to eliminate, as completely as possible, all pathogenic and also bacterial endotoxins from the final formulation of the active principle before preparation, in order to avoid unwanted and frequent, hazardous reactions to said toxic agents .

This requirement is much more noticed in the manufacture of diagnostic contrastographic formulations where there is often a need to administer large volumes of highly concentrated solutions of said formulations to the patient.

Among the various diagnostic "imaging" techniques (x-ray, NMR, echography) it is worth mentioning, for example, the x-ray technique where the opacifying contrast agent is preferably represented by a non-ionic iodine-containing aromatic compound.

In order to provide sufficient contrast, injectable solutions of these compounds are usually very concentrated, and when the approximate value of 80% by weight by volume is administered, for example by the intravenous route, in volumes that can reach 250 ml and more per single dose.

Another chosen route of administration for these compounds is, for example, the intrathecal route for tests involving nervous tissue, and in this regard it is well known that this type of tissue proves to be very much more sensitive than others to toxic agents (up to 1,000 times more sensitive). .

It is therefore clear that especially in injectable solutions of these compounds the presence of bacterial endotoxins must be as low as possible.

Among the liquid depyrogenation techniques in common use in industry, the use of microporous filters and ultrafiltration membranes has now become widespread.

Such membranes are in all cases widely used with particularly satisfactory results for the treatment of water or for dilute solutions.

Unfortunately, the situation turns out to be very different when it is desired to subject contrast agent solutions to ultrafiltration such as, in particular, for non-ionic iodine-containing compounds, which are highly concentrated and viscous.

The problem is that due to the characteristics of these solutions, there is a need for very large filtration surfaces to remain within the range of feasible production times that are industrially acceptable. In contrast, smaller surfaces would greatly extend the filtration times.

Consequently, the required equipment is bulky and characterized by significant dead volumes where non-negligible amounts of unfiltered solution would be stagnant. At the end of each work cycle, this solution had to be discarded or recovered and processed separately in a suitable smaller equipment. All this has significant adverse effects on the total production costs and potentially also on the final quality of the product.

An obvious attempt to solve this difficulty consists in the use of helically wound membranes for tangential ultrafiltration (having a suitable porosity capable of blocking the passage of the bacterial endotoxins: for example, an average "cut-off" of 10,000 daltons) which is adapted in cartridges of relatively limited dimensions and able to work under pressure, a possibility which for technical reasons is not applicable to other filtration systems, such as for example those formed by so-called string filters, used industrially in this case. In this way, it should have been possible to achieve significant improvements both in terms of space and process speed.

However, it was unexpectedly found that the membranes which theoretically would have been the best, especially with regard to strength and service life characteristics, such as for example those that are polysulfone-based, were not only clogged within more or less short periods of time depending on the characteristics of the pharmaceutical preparation which was to be filtered, but in addition showed the property of weakening the real composition of the contrast medium's formulation. In fact, the membrane partially rejected the salt excipient (especially when said excipient is EDTA.Ca2Na), while the nonionic iodine-containing agent preferentially passes through. This phenomenon, which was completely unexpected and, according to the actual supplier of the membrane, unpredictable for pharmaceutical solutions of this type, made it impossible to use this method for the desired purpose.

Nor could the membrane's performance be restored

with frequent use of detergents, for example after each work cycle, since the previously mentioned phenomenon was already manifested after the passage of a few hundred liters of solution. Nor did it turn out to be possible to solve the problem

in an acceptable way by changing the type of filtering material. Finally, complex experimentation led to the identification of a class of membranes, mainly those based on cellulose, which allowed the desired pyrogen retention to be achieved without significantly impairing

the composition of the formulation. However, it was not possible to prevent said membrane from becoming clogged within a short time.

Insertion of the pre-filters upstream of the ultrafiltration unit proved similarly disappointing as these pre-filters, due to the special characteristics of high concentration and viscosity of the solutions, in addition to the very fine micropollutants contained in them, lost their effectiveness by becoming clogged early during the pressure conditions necessary to achieve acceptable pre-filtration times. It was possible to prevent this defect only by arranging a series of pre-filters connected in parallel, in which said filters were connected to each other by a complex bypass system whose function was to change the solution to be depyrogenated from one pre-filter to the next without in each case having to interrupt the process to replace the pre-filter cartridge that had become clogged. All this involved the construction of equipment that was complex and bulky, and the management of which was sophisticated and expensive. Furthermore, the final yield of the process in each case proved to be suboptimal due to the dead volume due to the prefiltration system. To describe the situation more clearly, a schematic description of the equipment is shown in Figure 1.

As indicated therein, the solution to be depyrogenated is driven from the feed tank A through the pre-filter to the collection tank D under pressure conditions that ensure total flow rates of 1200/1500 and further l/h, regardless of the pre-filter used (a significantly lower flow rate would not be acceptable in the general economy of the process involving excessively long total filtration time).

These high pressure conditions, especially with high viscosity solutions, caused rapid clogging of the pre-filter which would need to be changed on several occasions in each duty cycle. As a result, there would be an extension of the total time, loss of product and possibility of contamination.

The selection of a series of pre-filters (C1, C2, C3) connected in parallel and controlled by a diverter (B) which redirects the solution coming from A from one filter to the next, allows the completion of the work cycle at that time and under the working conditions that is desired, without having to interrupt the process.

Naturally, the disadvantages of this process are associated with the complexity of the pre-filtration system, with the space required to accommodate it and the high maintenance costs, taking into account that used filters must be removed and replaced with new ones. These problems assume even greater importance the more substantial the batch to be purified is, because the number of cartridges to be used for each cycle depends on both the working conditions (for example, the applied pressure and temperature) and the total volume of solution to be processed.

On the other hand, the possible alternatives consisted in choosing either a very much larger and more voluminous prefilter or a prefilter with significantly lower pressure values, none of the parameters being applicable in industrial processes involving batches with at least 800 - 1500 1 formulation.

The prefiltered solution is collected in another tank D from which it is later taken off and pumped to the filtration unit E according to procedures usually used in ultrafiltration. The pyrogenated filtrate ends up in a suitable collector where, before it is finished, it will be rehomogenized under agitation, while the residue, progressively enriched with pyrogens, is fed back to tank D, which is diluted and then recycled to the filter E until the time when the whole the process is complete.

It has now unexpectedly been found that it is possible to solve, in an optimal way, the above-discussed problems by virtue of a method which can be carried out each with the help of a very simple filtering equipment of moderate dimensions which equipment can be controlled in an economical way and is able to provide a high total yield both in terms of quality and quantity.

The method of the invention consists of the following steps:

a) pre-filtration of the solutions by means of a microfiltration unit, which comprises one or more filtration cartridges of decreasing porosity connected in series with each other; b) pumping the solution from step (a) into an ultra-filtration unit, which consists of at least one filtration module

equipped with tangential ultrafiltration membranes having a porosity such that bacterial endotoxins are denied passage, wherein the tangential ultrafiltration membranes are cellulose-based and have an average "cut-off" of 10,000 daltons, whereby a permeate and a retentate are obtained, the retentate, which is enriched with pyrogenic content is recycled directly to the solution that comes from step a) and the depyrogenated permeate that complies with the limits set by the pharmacopoeia for the pyrogenic content is collected in a collector where it is homogenized by stirring before it is packaged/finished.

The method of the invention can be easily carried out using the equipment, schematically illustrated in Figure 2, which is extremely compact because it only uses a single pre-filter unit C and unexpectedly does not need a tank to collect the pre-filtrate. The pre-filter can take different forms, for example one or more filtering cartridges with decreasing porosity connected in series with each other. For example, a preferred configuration may consist of two filter cartridges of 1u and 0.22^ respectively. Equally preferred is, for example, a pre-filter composed of a single combined filtration cartridge, that is, one having decreasing porosity, with an average porosity of 0.5^. Essentially, the solution to be depyrogenated is driven through the prefilter C by virtue of a moderate pressure applied from the outside of the tank A (acceptable values are in the range from 1 to 3 atm, preferably from 1.5 to 2.5 atm).

When it comes from the prefilter, the solution is pumped directly to the ultrafiltration unit: the depyrogenated permeate is collected in a suitable collector equipped with stirring, and the retentate is recycled directly countercurrently by the pump controlling the ultrafiltration, to be mixed with the solution passing out from the prefilter. The ultrafiltration unit can be of varying composition: one of the preferred configurations can, for example, consist of a plurality of filtering modules (housing), in turn consisting of one or more filtering cartridges, said housing being able to work simultaneously or individually depending on the amount of solution to be filtered. The membranes that are preferably used are those that are able to prevent a significant weakening of the composition of the formulation during the process (for example that allow the preferential passage of one or more constituents compared to the others) and that have a porosity such that the passage of bacterial endotoxins are prevented.

From this point of view, cellulose-based membranes have proven to be particularly preferred, especially those of regenerated cellulose, with an average "cut-off" of 10,000 daltons. An absolutely non-limiting example of these is represented by spirally wound cartridges of regenerated cellulose S10Y10(<R>) and/or S40Y10(<R>) (Amicon).

The pressure across the membrane used on the ultrafiltration unit varies depending on the type of filter cartridge used and the characteristics of the solution to be filtered (for example, the concentration is a very important factor, thus the viscosity of said solution).

As a rule, completely acceptable results are obtained by using transmembrane pressures varying between 1 and 5 atm. When it is necessary to depyrogenate less viscous solutions, it will of course be possible to achieve high flow rates (and therefore shorter times) when lower transmembrane pressures are used.

The flow rates that are achievable can normally vary between 4 l/h per m<2> of the filtering surface and 70 l/h-m<2>, preferably between 6 and 55 l/h-rn2.

The operating temperature is another important parameter and is dependent on the thermal stability of the diagnostic formulation to be filtered and on the limits imposed by the filtration material. In the case of cellulose-based membranes, especially those of regenerated cellulose, it is for example possible to operate from 20°C to 55°C. Particularly preferred, in the case of highly concentrated and viscous solutions, is a temperature of about 50-54°C, preferably 52°C + 2°C, while in the case of less viscous solutions it is preferred to operate at temperatures of about 30°C.

An absolutely non-limiting example is represented by the filtration of batches of 100-200 1 of Iomeron (<R>) 150 (an injectable specialty containing the non-ionic iodine-containing contrast agent iomeprol in a concentration corresponding to a content of 150 mg/l per ml) in an AMICON SP150 + 52062 ultrafiltration unit equipped with S4010(<R> >ultrafiltration cartridge (Amicon) gives a total filtration surface of about 11 m<2>. By working at temperatures of 45°C + 5°C and using a transmembrane pressure which is varied from batch to batch from 1 to 4 atm, flow rates were obtained which were within the range between 12 and 45 l/h per m<2> with filtration times (for batches of 200 1) within the range between 0, 4 and 1.5 hours.

Another example of the invention can be represented by the depyrogenation of an industrial batch of 1,000 1 with

Iopamiro(<R>) 3 00 (an injectable specialty containing the nonionic iodine-containing contrast agent iopamidol in a concentration corresponding to a content of 3 00 mg/I per ml) performed in an Amicon SPM48O unit equipped with regenerated cellulose cartridges for a total filtering surface of about 45 m<2>, average "cut-off" of 10,000 daltons.

By operating at a temperature of 52°C + 2°C and using a transmembrane pressure of 3.5 atm, a flow rate of about -11 l/h per m<2> is achieved for a total filtration time of about 2 h.

The designed equipment as stated in claim 18's characterizing part proved to be surprisingly efficient especially because in the elimination of tank D (typical of an ultrafiltration process: as a common practice, where there are no prefiltration problems, the residue is recycled directly, in diluted form, to the feed tank, which is obviously not possible in the present situation), the retentate C is mixed directly with the flow coming from the pre-filter which causes an almost immediate increase in the concentration of toxins in the solution to be filtered. This fact would obviously weaken the efficiency of the filtration unit.

However, the efficiency of the process turns out to be optimal, and the lifetime of the cellulose filter turns out to be surprisingly long, as its greater structural fineness had initially greatly discouraged its continuous use for filtering highly viscous solutions, such as, for example, X-ray diagnostic solutions , and especially at temperatures that are very close to the operating limits described for said filter.

The fact that the process is a single stage process eliminates the wasted time to collect the pre-filtrate in tank D in Figure 1. It also proves possible to operate at moderate pressures with obvious advantages in terms of the safety of the equipment. A single-step process has therefore been created (as opposed to the one illustrated in Figure 1 which is essentially a two-step process) that is economical, fully compliant with the strictest regulatory standards, highly efficient and also complete in line with the requirements to show consideration for the environment because it eliminates the need to use detergents to clean and restore the filtration surfaces (a simple step of sanitizing surfaces, for example with baking soda, is sufficient). This provides a drastic improvement from the environmental impact side. Furthermore, this also removes the need to eliminate all residual traces of detergent and the need to then analytically certify its absence. All this also brings clear advantages in terms of costs and quality of the finished product.

If required, it is also possible to add at the outlet, preferably downstream from the collector/mixer of the filtrate (not indicated in Figure 2), a further sterilization filter with 0.2 µ or even less (F, indicated in the sketched the zone in figure 2), and thereby a final solution is obtained which is homogeneous and completely sterile ready to be made ready.

The flow rate remains substantially constant throughout the duration of the process. In this way, it becomes possible to process preparations up to 800-1,500 1 in a moderate time (1.5-5 h.), with yields of up to 97-98%, while obtaining a product that is in full compliance with the strictest pharmacopoeial limits.

The method and equipment of Figure 2 have been found to be particularly useful for the depyrogenation of diagnostic injectable pharmaceutical formulations as set forth in claim 23. Radiopaque diagnostic formulations comprising, as a contrast agent, a non-ionic iodine-containing compound, a mixture of iodine-containing compounds or either of monomeric or of dimeric types, have been shown to

be particularly preferred.

Some examples of iodine-containing radiopaque contrast agents, whose injectable formulations can be depyrogenated using the method and equipment of the invention, can be selected from the following monomeric and dimeric compounds and mixtures thereof: iopamidol, imeprole, iohexol, ioversol, iopentol, iopromide, ioxolane , iotriside, iobi-tridol, iodixanol, iofratol, iotrolan, iodecimol, iopirole, iopiperidol.

Equal preference has been shown to have to be attributed to injectable formulations of contrast agents for NMR "imaging" as set forth in claim 24, usually consisting, as contrastographic ingredients, of chelates of paramagnetic metal ions (such as, for example, Gd<3+>, Mn<2+>, Fe<3>+, Eu<3>+, Dy<3*> etc.) with chelating agents of various types (such as, for example, linear or cyclic polycarboxylic poly-amino acids, and derivatives and salts thereof , polyaminophosphonic or polyaminophosphinic acids thereof, etc.).

Some examples of contrast agents of this type can be selected from among the following: chelate of Gd<3+> with diethylenetriamine pentaacid (Gd-DTPA), chelate of Gd<3+> with 1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid (Gd-DOTA), chelate of Gd<3+> with [10-(2-hydroxypropyl)-1, 4, 7,10-tetra-azacyclododecane-1,4,7- triacetic acid (Gd-HPD03A), chelate of Gd<3+> with 4-carboxy-5, 8,11-tris(carboxymethyl)-1-phenyl-2-oxa-5,8,11-triazatridecano-13-acid ( Gd-BOPTA) , chelate of Gd<3+> with N-[2-[bis(carboxymethyl)amino]-3-(4-ethoxy-phenylDpropyl]-N-(2- [bis(carboxymethyl)amino] ethylglycine ( Gd-EOB-DTPA) , chelate of Gd<3+> with N,N-bis [ (carboxy-

methyl) [ (methylcarbonyl) methyl] amino] ethyl] -glycine (Gd-DTPA-BMA) , chelate of Gd<3+> with (a, a' , a' ' , a' ' ■) -tetramethyl-1, 4,7,10-tetraazocyclododecane-1,4,7,10-tetraacetic acid (Gd-DOTMA), chelate of Mn<2+> with N,N1 -bis(pyrodoxal-5-phosphate)ethylene-diamine-N ,N'-diacetic acid (Mn-DPDP) and salts and derivatives thereof, such as for example those of amide or

ester type.

Claims (24)

1. Procedure for depyrogenation of injectable solutions of pharmaceutical formulations with contrast agents for diagnostic imaging, characterized in that it mainly comprises the following steps: a) for filtering the solutions by means of a microfiltration unit, which comprises one or more filtering cartridges with decreasing porosity connected in series with each other; b) pumping the solution from step (a) into an ultrafiltration unit, which consists of at least one filtration module equipped with tangential ultrafiltration membranes having a porosity such that bacterial endotoxins are denied passage, wherein the tangential ultrafiltration membranes are cellulose-based and have an average "cut-off " of 10,000 daltons, whereby a permeate and a retentate are obtained, the retentate, which is enriched with pyrogenic content, is recycled directly to the solution coming from step a) and the depyrogenated permeate which complies with the limits set by the pharmacopoeia for the pyrogenic content is collected in a collector where it is homogenized by stirring before it is packaged/finished. 2. Method according to claim 1, characterized in that the pre-filter comprises two filtration cartridges, which are connected in series with porosity of 1^ and 0.22^ respectively. 3. Method according to claim 1, characterized in that the pre-filter comprises a simple composite filter cartridge with decreasing porosity which has an average porosity of 0.5 µm. 4. Method according to claim 1, characterized in that the injectable pharmaceutical solution with contrast agent is passed through the pre-filter under a pressure which is variable between 1 and 3 atm. 5. Method according to claim 1, characterized in that the ultrafiltration unit comprises a number of filtration modules which are able to operate simultaneously or individually. 6. Method according to claim 1, characterized in that the ultrafiltration membranes are made of regenerated cellulose. 7. Method according to claim 6, characterized in that the preferred ultrafiltration membranes are selected from spirally wound cartridges S1OY10 and S40Y10 (Amicon). 8. Method according to claim 1, characterized in that the transmembrane pressure applied to the ultrafiltration unit allows an outflow rate of the permeate which is variable between 4 and 70 l/h per m<2>. 9. Method according to claim 8, characterized in that said transmembrane pressure is variable between 1 and 5 atm. 10. Method according to claim 1, characterized in that the operating temperature is variable between 20°C and 55°C throughout the process. 11. Method according to claim 1, characterized in that the diagnostic pharmaceutical formulation comprises, as active principle, at least one non-ionic iodine-containing radiopact agent. 12. Method according to claim 11, characterized in that the radiopaque agent is iopamidol. 13. Method according to claim 11, characterized in that the radiopaque agent is iomeprol. 14. Method according to claim 11, characterized in that the formulation comprises a mixture of monomeric and dimeric non-ionic iodine-containing radiopaque agents. 15. Method according to claim 11, characterized in that the diagnostic pharmaceutical formulation comprises, as active principle, at least one contrastographic agent for NMR "imaging". 16. Method according to claim 15, characterized in that the contrastographic agent is a chelate of the ion of a paramagnetic metal. 17. Method according to claim 16, characterized in that the paramagnetic chelate is selected from: Gd-BO PTA and Gd-HPD03A and salts thereof. 18. Equipment for depyrogenation of, by means of tangential ultrafiltration, an injectable solution with a pharmaceutical diagnostic formulation of a contrast agent, according to claim 1, characterized in that the equipment mainly comprises: a feed tank (A), containing the solution; a pre-filtration unit (C), comprising one or more filter cartridges of decreasing porosity, connected in series with each other, through which the solution from (A) is passed; an ultrafiltration unit (E) and pumping means for pumping the solution emerging from (C) into the ultrafiltration unit (E), whereby a retentate and a permeate are obtained; means to recycle the retentate from the unit (E), said retentate is enriched with pyrogens directly into the solution coming out of (C), upstream of the pumping means; a collector, equipped with agitators, where the depyrogenated permeate from unit (E) is collected and homogenized before it is packaged/finished. 19. Equipment according to claim 18, characterized in that the pre-filtration unit (C) comprises two filter cartridges, which are connected in series with porosity lu and 0.22^ respectively, or a simple composite filter cartridge with decreasing porosity which has an average porosity of 0.5^. 20. Equipment according to claim 18, further characterized in that a sterilization filter (F) with porosity 0.2U or less is placed downstream of the collector, whereby the final depyrogenated and homogenized injectable solution is completely sterilized before it is packaged. 21. Equipment according to claim 18, characterized in that it is used for depyrogenation of radiopaque injectable diagnostic solutions. 22. Equipment according to claim 18, characterized in that depyrogenation of injectable diagnostic solutions is used for NMR "imaging". 23. Depyrogenated radiopaque injectable diagnostic solutions, characterized in that they are obtained according to the method in claim 1. 24. Depyrogenated injectable diagnostic solutions for NMR "imaging", characterized in that they are obtained according to the method in claim 1.